Medications and other medical articles designated for certain patients, whether prescription or over-the-counter, are often stored in cabinets that may or may not be refrigerated. Accurate inventory tracking of medical articles is imperative to be sure that the needed medical articles are where they should be, that there are enough of them, and when used, that they are accounted for. Other reasons for tracking medical articles include monitoring expiration dates, recalls, and various other factors. Detection of supply depletion is also a purpose of tracking medical articles. Such cabinets may consist of refrigerators ranging in size from quite small to quite large, to non-refrigerated cabinets, to cabinets having a plurality of stacked drawers, to single trays each of which has a predetermined collection of medical articles. Containers may be locked or unlocked. Locked containers may include electrically-controlled mechanical locks that are opened by matching the identification of a user with authorized users contained in a database. Other containers for storing or transporting medical articles are encountered in a healthcare environment.
In another system becoming more in demand, medical articles are tracked from the manufacturer's facility to delivery at the healthcare facility, and all through the healthcare facility until the medical articles are either administered to a patient or disposed of in some other way.
An important use of such wireless tracking systems is to be sure that the correct patient receives the correct medication. Positively identifying the patient with an identification device, positively identifying a medication with a wireless tracking device, and using a database that ties the two together can be a highly effective system in avoiding medication errors.
Among the current systems being used for the tracking of items, the barcode tracking system is wireless and has advantages. Wireless barcode tracking systems continue to present a useful alternative, especially in retail stores and other areas where use of a line of sight reader does not present a problem. However in the healthcare field where medical cabinets are used, a line of sight system is less preferable. Some cabinets store many medical articles and reading each one by scanning it with a barcode reader can involve too much time for busy healthcare personnel. Instead, a wireless system that does not require a line of sight tracking system to identify medical articles would be preferable.
In the healthcare field, a radio frequency identification (“RFID”) tracking system has been found to excel. The RFID system does not require line of sight to make the identification. RFID systems typically include RFID stickers or labels, i.e., a sticker or label that includes an RFID tag, affixed to the inventory item, e.g., bottles, vials, boxes, syringes, bandages, etc. In a predominant system available today, each RFID tag has a unique identification number.
Each medical article has an RFID tag attached and the identification number of the RFID tag is entered into a database and correlated with the name of the medical article to which the tag is attached. A processor programmed to read the database matches that RFID tag identification number to the medical article to which it was originally attached so that the particular medical article can be determined to be present in the container. The database often includes an array of the data regarding the medical article to which the RFID tag is attached, such as the name, dose, manufacture date, expiration date, temperature requirements, and other data.
In another embodiment, the RFID tag itself has a programmable memory that can be programmed with identifying data about the nature of the very medical article to which it is attached thereby immediately identifying the medical article without the need to refer to a database. EPC Gen2/ISO 18000-63 standard RFID tags are available in many different configurations. Some of these tags are delivered preprogrammed with a 48-bit read-only write-protected unique ID. These preprogrammed tags with a unique ID are the same price as those tags that do not have a preprogrammed unique ID. This system also has advantages.
RFID tags may be incorporated into or attached to articles to be tracked. In some cases, the tag may be attached to the outside of an article with adhesive, tape, or other means and in other cases, the tag may be inserted within the article, such as being included in the packaging, located within the container of the article, or sewn into a garment. Some RFID tags are manufactured with a unique identification number which is typically a simple serial number of a few bytes with a check digit. In some cases, no check digit is stored, the error correction codes are generated on the fly by the RFID tag and reader. This identification number is incorporated into the tag during manufacture. The user cannot alter this serial/identification number and manufacturers guarantee that each serial number is used only once. This configuration represents the low cost end of the technology in that the RFID tag is read-only and it responds to an interrogation signal only with its identification number. Typically, the tag continuously responds with its identification number. Data transmission to the tag is not possible. These tags are very low cost and are produced in enormous quantities. There are no EPC Gen2/ISO 18000-63 standard based RFID tags currently available in the configuration described above. The simplest RFID tags conforming to these standards include a minimum of 96 bits of programmable memory.
Such read-only RFID tags typically are permanently attached to an article to be tracked and, once attached, the serial number of the tag is associated with its host article in a computer database. For example, a particular type of medicine may be contained in hundreds or thousands of small vials. Upon manufacture, or receipt of the vials at a health care institution, an RFID tag is attached to each vial. Each vial with its permanently attached RFID tag will be checked into the database of the health care institution upon receipt. The RFID identification number may be associated in the database with the type of medicine, size of the dose in the vial, and perhaps other information such as the expiration date of the medicine. Thereafter, when the RFID tag of a vial is interrogated and its identification number read, the database of the health care institution can match that identification number with its stored data about the vial. The contents of the vial can then be determined as well as any other characteristics that have been stored in the database. This system requires that the institution maintain a comprehensive database regarding the articles in inventory rather than incorporating such data into an RFID tag.
An object of the tag is to associate it with an article throughout the article's life in a particular facility, such as a manufacturing facility, a transport vehicle, a health care facility, a storage area, or other, so that the article may be located, identified, and tracked, as it is moved. For example, knowing where certain medical articles reside at all times in a health care facility can greatly facilitate locating needed medical supplies when emergencies arise. Similarly, tracking the articles through the facility can assist in generating more efficient dispensing and inventory control systems as well as improving work flow in a facility. Additionally, expiration dates can be monitored and those articles that are older and about to expire can be moved to the front of the line for immediate dispensing. This results in better inventory control and lowered costs.
RFID tags may be applied to containers or articles to be tracked by the manufacturer, the receiving party, or others. In some cases where a manufacturer applies the tags to the product, the manufacturer will also supply a respective database file that links the identification number of each of the tags to the contents of each respective article. That manufacturer supplied database can be distributed to the customer in the form of a file that may easily be imported into the customer's overall database thereby saving the customer from the expense of creating the database.
Many RFID tags used today are passive in that they do not have a battery or other autonomous power supply and instead, must rely on the interrogating energy provided by an RFID reader to provide power to activate the tag. Passive RFID tags require an electromagnetic field of energy of a certain frequency range and certain minimum intensity in order to achieve activation of the tag and transmission of its stored data. RFID tags may be activated by electric field energy and by magnetic field energy. Another choice is an active RFID tag; however, such tags require an accompanying battery to provide power to activate the tag, thus increasing the expense of the tag and making them undesirable for use in a large number of applications.
Depending on the requirements of the RFID tag application, such as the physical size of the articles to be identified, their location, and the ability to reach them easily, tags may need to be read from a short distance or a long distance by an RFID reader. Such distances may vary from a few centimeters to ten or more meters. Additionally, in the U.S. and in other countries, the frequency range within which such tags are permitted to operate is limited. As an example, lower frequency bands, such as 125 KHz and 13.56 MHz, may be used for RFID tags in some applications. At this frequency range, the electromagnetic energy (“EM”) is less affected by liquids and other dielectric materials, but suffers from the limitation of a short interrogating distance. At higher frequency bands where RFID use is permitted, such as 915 MHz and 2.4 GHz, the RFID tags can be interrogated at longer distances, but they de-tune more rapidly as the material to which the tag is attached varies. It has also been found that at these higher frequencies, closely spaced RFID tags will de-tune each other as the spacing between tags is decreased.
Providing an internal RFID system in such a cabinet can pose challenges. Where internal articles can have random placement within the cabinet, the RFID system must be such that there are no “dead zones” that the RFID system is unable to reach. In general, dead zones are areas in which the level of coupling between an RFID reader antenna and an RFID tag is not adequate for the system to perform a successful read of the tag. The existence of such dead zones may be caused by orientations in which the tag and the reader antennae are in orthogonal planes. Thus, articles placed in dead zones may not be detected thereby resulting in inaccurate tracking of tagged articles. Fresnel zones (null energy and high energy regions) occur when reflected RF energy collides with transmitted energy or other reflected energy waves. The most common null energy region (dead zone) occurs when reflected energy collides with transmitted energy at ninety degrees out of phase.
Often in the medical field, there is a need to read a large number of tags attached to articles in such an enclosure, and as mentioned above, such enclosures have limited access due to security reasons. The physical dimension of the enclosure may need to vary to accommodate a large number of articles or articles of different sizes and shapes. In order to obtain an accurate identification and count of such closely-located medical articles or devices, a robust electromagnetic energy field must be provided at the appropriate frequency within the enclosure to surround all such stored articles and devices to be sure that their tags are all are activated and read. Such medical devices may have the RFID tags attached to the outside of their containers and may be stored in various orientations with the RFID tag (and associated antenna) pointed upwards, sideways, downward, or at some other angle in a random pattern.
Generating such a robust EM energy field is not an easy task. Where the enclosure has a size that is resonant at the frequency of operation, it can be easier to generate a robust EM field since a resonant standing wave may be generated within the enclosure. However, in the RFID field the usable frequencies of operation are strictly controlled and are limited. The U.S. FCC, and other national authorities around the world, have established regulations that define the frequency bands in which wireless systems (RFID, WiFi™, Bluetooth, etc.) can operate license free. The UHF band in the U.S. extends from 902.5 MHz to 928.0 MHz and was selected for RFID technology because of the low attenuation of this frequency in free space (i.e., it provides the longest read distance and therefore is ideal for supply chain management). It has been found that enclosures are desired for the storage of certain articles that do not have a resonant frequency matching one of the allowed RFID frequencies. Thus, a robust EM field must be established in another way.
Once activated, the RFID tags transmit their respective identifications that are received by a receive antenna and conducted to an RFID reader to determine their presence in the container. This is commonly referred to as reading the RFID tag. In order to read the tags, an injection probe or probes are placed within a storage cabinet along with a receive antenna or antennas. In another embodiment, the injection probe and receive antenna are the same device and both functions are accomplished by switching the device between an energy injection mode and an energy receive mode. The receive antennas are interfaced with the RFID reader, which can be permanently mounted at the cabinet. The system sends activating energy, also known as interrogation signals, via the injection probe which emits that activating energy in the storage container. The activating energy is strong enough (also described as having a high enough power level) to activate the passive RFID tags. Those activated tags then respond with their stored data. The receive antennas receive the responsive data from the RFID tags and this data is forwarded to the RFID reader.
In the healthcare environment, cabinets enabled with RFID tracking systems employ a Faraday cage, which is a conductive chamber completely surrounding the container area. The Faraday cage prevents the RFID tracking system located inside the container from reading RFID tags outside the container area which would cause an error. The Faraday cage also preserves the RF energy within the enclosure for use in identifying RFID tags.
Various problems exist with RFID tag activation in an enclosed space. As discussed above, there are often nulls or dead spaces or dead zones in which tags will not receive enough RF activating energy to be activated. Placing many RFID activation probes throughout the enclosed container will increase the chances of activating all RFID tags, but at the cost of more wires, probes, and antennas. Use of a large quantity of antennas also results in larger enclosures and increased read process time. Increasing the power level in the container may help but there are limits imposed by FCC on the power level. For example, in the U.S., a maximum transmit power of 4 watts (EIRP—equivalent isotopically radiated power) is allowed. Additionally, power levels that are too high may increase the chances of reading RFID tags located outside the container even though the Faraday cage exists. It has been found that Faraday cages used as containers that must allow access may leak the activation energy outside the container and the tracking system may detect RFID tags on medical articles located outside the container thereby causing a tracking error.
Another problem is the effect that liquids have on an RFID reader. Liquids may actually absorb the activation energy resulting in the failure to activate an RFID tag. Other errors are caused by tags next to each other (tags positioned in close proximity to or directly against one another) detuning each other such that they are not activated by the RF activation field. Many such conventional designs can suffer from poor results obtained due to the static nature (tag positions are fixed) of the interrogations. In an application where the field is static, a tag may lie in a RF null created by multipath, resulting in a failed interrogation.
Further, many conventional solutions use the traditional combined transmit/receive antenna configuration. In this arrangement, a single wireless EM conduction device operates as both a transmit antenna and as a receive antenna. This configuration works well in traditional applications where the RFID reader antenna radiates into open space and objects are in the far-field region of the antenna for minimum RFID reader antenna detuning. Far-field is described as a boundary region where the angular field distribution of the antenna is essentially independent of distance from the source. However, in applications where the RFID tags to be read are in the interior space of a container that is within the near-field of the transmitting device, problems can arise. Reflections of the transmitted energy can establish the null zones within that container. For purposes of discussion herein, the wireless EM conduction device for the interior of a container is referred to as an “injection probe” because it is injecting activating RF energy into a closed space. In a case such as this, i.e., where the target space is closed, the traditional combined transmit/receive antenna approach and combined transmit and receive systems can encounter problems in activating an RFID tag that falls within a null zone.
As RFID tagged products enter the RFID reader antenna's near-field region, it has an adverse effect on the RFID reader's antenna tuning resulting in reduced RFID reader receiver sensitivity. This results in RFID reader antenna detuning and presents a challenge for the RFID reader's receiver in terms of energy reflected back into the RFID reader receiver competing with energy reflected back by the tagged items. Still further, RF signal propagation in contained environments is not well defined, with huge amplitude variations in resonant versus null locations within a drawer or chamber. When RFID tags are placed in a chamber's null locations, the tags cannot be powered and cannot be read/interrogated, ultimately causing errors in tracking medical articles.
Another problem exists when a tag is in its minimum field strength (such as between two transmitting antennas) with respect to its ability to turn on and participate in the interrogation. When this occurs the RFID reader may be unable to detect the tags' faint responses resulting in a failed interrogation. This is a common problem in a high product/tag density application where high concentration of items exists within the RF Tx and Rx paths. A similar problem with conventional solutions occurs when the items being tracked include large amounts of liquids. Conventional RFID cabinet systems typically use the electric field to communicate to passive RFID tags. Depending on the frequency used, some frequencies can be greatly attenuated by liquid items within the container resulting in a failed interrogation due to insufficient field strength. To lessen such effects, some manufacturers use larger RFID tags so that they will be more immune to detuning caused by a large number of tags located near each other. Also, it is thought that larger tags somewhat overcome the detuning of liquids. However, larger tags result in difficulty of handling the medications. This is discussed further below.
The above cause great difficulties for those RFID systems that are designed and developed to track RFID tags on items in the near field (distances less than approximately one wavelength from the antenna). The wavelength for electromagnetic energy of 915 MHz is 12.91 inches (32.77 cm), which is typical for RFID-enabled enclosures employed for storing medication, such as drawer systems, metal cabinets, refrigerators, and freezers. Integrating antenna systems in metallized or shielded enclosures used for tracking stored items tagged with RFID tags or smart labels, such as refrigerators, freezers, drawers, cabinets, etc., presents challenges due to the large amounts of energy that reflect off the enclosure walls and any metallized element inside the enclosure. Irrespective of energy reflections inside of a metallized enclosure it is difficult to set up electromagnetic waves in volume-restricted metallized enclosure, especially those enclosures that are non-resonant at the frequency of interest.
FIG. 3 shows what is called an RFID “flag” tag. The tag, which has commonly been in use for many years, includes a “flag” portion 72 on which is mounted an RFID device 76, and a mounting portion 74 that comprises a clear base on which a layer of clear adhesive is deposited. The mounting portion is adhered to the vial of medication for example. Because the mounting portion is clear, the label 75 placed on the vial by the manufacturer can be read through the mounting portion thus not obscuring expiration dates, dose size, name of the medication, name of the patient, and any other data placed on the vial. The commonly-used flag tags that are relatively large and consequently unwieldy. They take up excessive space in a storage container, interfere with each other during handling, and are difficult to handle. These more common tags are in widespread use because they contain a much larger RFID tag coupling device (antenna). This is necessary for many manufacturers of tracking systems because the larger-sized RFID tag coupling devices are able to collect more activating RF energy in those tracking systems that are inefficient and have dead zones or “weak zones.” FIG. 4 on the other hand shows the smaller-sized RFID flag tags that are preferable. Medications on which such smaller-sized tags are mounted are easier to handle, take less room, and are easier to store in containers. Even though the users of RFID tracking systems prefer the smaller RFID tags, many manufacturers cannot use them because they will not be activated with their RFID tracking systems and tracking errors will result.
Typical antennas used in RFID applications are microstrip antennas, patch antennas, and wire-based antennas. Although these types of antennas perform well for far field applications, they can generate null areas or regions, or low power (weak) areas or regions of activating RF energy at localized points in the near field due to the large aperture or effective area of the antenna. In addition, these antennas radiate an energy wave that is more linear than circular, which can result in loss of RFID tag interrogation energy due to the tag being cross polarized when positioned in the near field.
Tracking small form factor medications in small non-resonant enclosures requires smaller RFID tag sizes in order for the tagged items to fit easily into a tray or drawer pockets without impeding the loading of medications, dispensing of medications, or the opening and closing action of the drawer, container, or enclosure in which the medications are stored. Certain small form-factor RFID tags that operate in the 915 MHz industrial, scientific, and medical (“ISM”) radio bands include both a magnetic antenna loop/feature and a folded dipole so that both magnetic and electrical field energy can be harvested to operate the RFID tag. By definition, the RFID tags attached to small medication form factors stored in small non-resonant enclosures will be in close proximity (near field at 915 MHz) to the activating RF energy injection probes.
Certain antennas do not perform well under the difficult conditions of a relatively small container. For example, thin profile microstrip antennas have narrow bandwidth and poor radiation efficiency with a lossy substrate and therefore these planar patch antennas are not a good choice for a low cost solution. Additionally, a relatively large size of a microstrip antenna is required for performance at a frequency of around 900 MHz which makes it undesirable in most applications where space is at a premium.
Hence, those of skill in the art have identified a need for using a much smaller RFID flag tag on medical articles to be stored in a container, for using less power to activate all RFID tags in a container, and for having a much higher success rate of tag activation and reading. The present invention fulfills these needs and others.